This invention relates to filter media, and is directed particularly to expandible accordian-shaped filters which may be used in air filtration systems of the high efficiency type. An example of such a system is disclosed in the above-identified U.S. Pat. No. 3,789,589.
In that patent, the air filter comprises a self-supporting body of suitable material such as paper or other fibrous material. The body is reverse folded into an accordian-shaped member. The body may be collapsed into a small volume for ease of shipping and disposal. It may also be expanded for insertion into a supporting assembly which includes a plurality of fingers for holding the pleats against collapse.
As also disclosed in that patent, a spaced pair of narror strips of cloth or the like extend across the end portions of the filter body with the strips being secured to the pleat folds in a manner so that, when the body is expanded, the pockets are of a uniform width.
It has been found that the securement means between the strips and pleat folds, which was usually in the form of an adhesive, was not completely reliable. Separation of the strip from some of the folds has caused difficulties in installing the filter media into its support assembly and in the placement of the supporting fingers.
The present invention is directed to a substantially improved media wherein the previous type of spacing strip is replaced with an elongated string-like member which passes through a series of openings formed in the pleat walls. The openings are smaller in diameter than that of the elongated member when the latter is in a relaxed condition so that friction between the opening edges and the member fixedly holds the pleat walls in position along the member. The positioning of the walls on the member is such that the folds will be equally spaced when the filter body is in expanded condition. In a preferred form of the invention, the string-like member comprises one or more strands of fluffy yarn which is easily variable, both in diameter and length.